Paper-based microfluidic patterns have been demonstrated in recent literature to have a significant potential in developing low-cost analytical devices for telemedicine and general health monitoring. This study reports a new method for making microfluidic patterns on a paper surface using plasma treatment. Paper was first hydrophobized and then treated using plasma in conjunction with a mask. This formed well defined hydrophilic channels on the paper. Paper-based microfluidic systems produced in this way retained the flexibility of paper and a variety of patterns could be formed. A major advantage of this system is that simple functional elements such as switches and filters can be built into the patterns. Examples of these elements are given in this study.

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ABSTRACT:The internal and external curved surfaces of polysulfone hollow fiber membranes were characterized by atomic force microscopy (AFM), contact angle measurement (CAM), and scanning electron microscopy (SEM) with the aim of improving the membrane surface properties for blood compatibility. Novel approaches were applied to evaluate a number of properties, including the roughness, pore size, nodule size, and wettability of the surfaces of the hollow fibers. CAM studies were carried out by directly observing the liquid meniscus at the surfaces of hollow fibers. Observation of the meniscus and measurement of the contact angle became possible by using an imaging system developed in our laboratory. AFM and SEM studies were also conducted on the surfaces of the hollow fiber membranes by cutting them at an inclined angle. The effect of the molecular weight of poly(ethylene glycol) (PEG) in the polymer blend on the surface properties of the hollow fibers was studied. Increasing the PEG molecular weight increased the average pore size whereas it decreased the contact angle. The contact angle depended on the microscopic surface morphology, including nodule size and roughness parameters. The theoretical prediction along with the experimental data showed that the measured contact angle would be greater than the value intrinsic to the membrane material because of the formation of composite surface structures.

We employ an elementary model for the distribution of electronic states to develop a quantitative theory of equilibrium occupation statistics in disordered semiconductors. In particular, assuming Fermi–Dirac statistics and charge neutrality, we determine how the Fermi level position varies with temperature for various amounts of disorder and various dopant concentration levels, disorder being represented by the breadth of the tails in the conduction band and valence band distributions of electronic states. We find that as the disorder is increased the Fermi level is pulled towards the intrinsic Fermi level. An explanation for this result is provided.

The spreading of solid powder over a liquid surface is a prevalent phenomenon encountered in many industrial processes such as food and pharmaceutical processes.The driving force for powder spreading over a liquid surface is not clearly understood.The Marangoni effect due to a temperature gradient and the spreading coefficient for solid powder over liquid ( S/L ) have both been proposed as causes for powder spreading over liquids. The proposed  S/L was based on the same form of the spreading coefficient for a liquid over a solid surface ( L/S ). Whereas  L/S has a clear thermodynamic definition, the spreading coefficient of solid powder over liquid,  S/L , which was defined by simply interchanging the subscripts of the interfacial energy terms, has not been thoroughly analysed. Our experimental results showed that the spreading behaviour of solid powders over liquids cannot be explained or predicted by  S/L . In this study we focus on problems associated with the  S/L . Through a thermodynamic analysis we conclude that the existing parameter  S/L is unable to predict the spreading behaviour of solid powder on liquid surface, since the interfacial energy approach does not capture the actual physical process of powder spreading over liquid surface. A closer examination of the powder spreading process reveals the *Manuscript Click here to view linked References